The present invention relates to a method for allocating calls given via landing call devices of elevators belonging to an elevator group so that all calls will be served.
When a passenger wants to have a ride on an elevator, he/she will issue a call for an elevator by pressing a landing call button mounted at the floor. The control system of the elevator group receives the call for an elevator and tries to figure out which one of the elevators in the elevator group will be best able to serve the call. The activity is termed call allocation. The problem to be solved by allocation is how to find the elevators to serve landing calls so as to minimize a preselected cost factor. Allocation may aim at minimizing passengers"" waiting time, passengers"" traveling time, the number of times the elevator will stop.
Traditionally, to establish which one of the elevators would be appropriate to serve a call, the reasoning is carried out individually for each case using complicated conditional structures. The final aim of this reasoning is to minimize a cost factor describing the operation of the elevator group, typically e.g. the call time or the average waiting time of the passengers. As the elevator group works in a complicated state space, the conditional structures are also complicated and they cannot cover all possible situations. Thus, there appear situations in which the control is not functioning in an optimal way. Likewise, it is difficult to take the elevator group into consideration as a whole. A typical example of this is the traditional collective control, in which a landing call is served by the one of the elevators which is traveling in the direction toward the call at the closest distance from the calling floor. This simple optimization principle, however, leads to aggregation of the elevators, which means that the elevators are traveling in a front in the same direction, and therefore to a fall in the performance of the elevator group as a whole.
An attempt to determine the cost factors for all possible route alternatives is likely to require a computing capacity exceeding the capacity of the existing processors. If the number of calls to be served is C and the building has L elevators, then the number of different route alternatives will be N=Lc. Since the number of route alternatives increases exponentially as the number of calls increases, it is impossible to systematically consider all route alternatives even in a small elevator group. This has been a limitation hampering the application of route optimization in practice. On a general level, allocation methods can be classified into at least three approaches when the matter is considered from the passengers"" point of view: continuous, immediate and target-oriented allocation methods. In continuous allocation of landing calls, landing calls are allocated to an elevator car at an instant when the elevator assigned to a given landing call is still able to stop at the floor in question. Until that instant, the distribution of active landing calls among the elevator cars can be changed freely. Continuous allocation is typically used e.g. in Europe. However, for example in Asia, elevator systems are designed with the aim of allowing passengers to know immediately upon pressing a landing call which elevator is going to serve them. In this case, the landing calls issued are allocated immediately to the elevators that are to serve them. Once allocated, a call should not be switched to another elevator. Target-oriented allocation again is perceived by the passenger above all as a different user interface between the passenger and the elevator system, in which the passenger is informed individually via a separate interface as to which elevator is going to serve him/her. With the solution of the invention, the uncertainty as to the right elevator is reduced and passengers can walk tranquilly to the area in front of the elevator which is going to serve them. The control unit used is a unit controlling the fixation of calls. The solution of the invention also improves traveling comfort and indirectly also the performance of the system.
As for the features characteristic of the invention, reference is made to the claims.
In the solution of the invention, an allocation unit finds the best routes for the elevators, in other words, makes the actual decisions as to which one of the elevator cars is to serve each call. A landing call-specific allocation suggestion is transmitted to a call fixation control unit, which registers each landing call as being reserved for the elevator car suggested for it. The landing call data from the allocation unit includes data giving, in addition to the elevator, also an estimated time of arrival (ETA) at the floor of issue of the landing call. While registering the landing call as being reserved for the suggested elevator car, the call fixation control unit sends a signaling command to this elevator, which will immediately perform signaling at the floor in question. In pure immediate-allocation, a landing call is immediately fixed for the elevator car allocated to serve it, but in the proposed method it is also possible to control the instant of fixation so that fixation will take place in a completely stepless manner. In this case, a parameter is used which determines how many seconds before the arrival of the elevator the landing call is to be fixed for the elevator car and signaled to passengers. Another alternative is to define the time in seconds after the entry of a landing call within which the call is to be reserved for an elevator car and signaled to passengers. By comparing the time of this parameter in the former case to the ETA time, the system decides whether the landing call is to be reserved for an elevator car or whether it shall be kept free to be allocated to any car in the elevator group. In the latter case, the parameter is compared with the length of time the landing call has been active. The value of both parameters can be varied e.g. according to traffic intensity and/or traffic type or according to time and date or a preliminary plan.
In case of special situations, the call fixation control unit must also be able to release one or more landing calls already reserved so as to allow the call(s) to be served by any other elevator car. Such situations include cases where an elevator is separated from the elevator group e.g. because of a technical failure, cases of activation of locking of an elevator, cases of an elevator car being loaded to full capacity and consequent possible bypassing of landing calls, cases of landing calls remaining active for an excessively long time, situations illogical from the point of view of the passengers, such as when an elevator (serving a car call) arrives at the floor of a landing call but then goes on traveling in the opposite direction relative to the passenger""s destination. When a landing call has to be released for one reason or another, the call fixation control unit makes an entry in its bookkeeping system to the effect that the landing call may be served by any one of the elevators (not necessarily the one which had been intended for it before). In this case, the control unit also sends to the elevator a signaling command concerning the landing call that will turn off the signal lights.
The action is based on limiting the search range of a route finding algorithm in the allocation unit. A control decision alternative or chromosome contains landing call-specific genes whose value indicates the elevator car that is to serve the landing call in question. Thus, the range of values of each individual gene is the same as the number of possible elevator cars that are able to serve the call. If the elevator group has e.g. eight elevators which are all able to serve the call, then the range of values for the gene will be eight. At the start of a search for a control decision, the allocation unit sends to the call fixation control unit an inquiry for each landing call, asking which elevator cars are able to serve the landing call in question. If the landing call is still free (unallocated), all cars can serve it and the final range of values for the landing call will equal the number of elevator cars, assuming that there are no other limitations, such as locked states. By contrast, if the call fixation control unit has reserved the landing call for one of the elevator cars, then the range of values for the gene will be one, and the only possible value will be the elevator car for which the call has been reserved. In practice, therefore, the reservation of the landing call limits the range of values of the gene to one possible value, so when an allocation decision is made, the landing call will always end up being allocated to the elevator car for which it has been reserved. If the landing call is free, e.g. one that has just appeared in the elevator system or that has been released because of a special situation, the allocation procedure will perform a search according to its own principles to find an optimal elevator car for the call and all other free landing calls. After a final control decision has been made, it is transmitted to the call fixation control unit, which will reserve the free landing calls for elevator cars according to the control decision.
The immediate landing call allocation method differs essentially from continuous allocation in that, instead of a single floor, there may be several floors to be signaled at the same time according to the service routes of the elevator cars.
The call fixation control unit takes care of reservation and release of landing calls as well as the commands for corresponding signaling. Reservation of landing calls means that the calls may only be served by a single car, and release of calls means that the landing calls may be served by any one of the elevators. An actual allocation decision is made by a genetic allocation method by limiting the range of values of landing call-specific genes in accordance with the status of call reservation, which is obtained from the call fixation control unit. If a landing call is free, then there are no limitations, but if it has been reserved, then the range of values for the gene is limited to one and the only value it can get is the elevator car reserved for it. The allocation decision is taken to the call fixation control unit, which reserves and controls the signaling.
An additional feature is the method is its flexibility for implementing a floating signaling time, regarding which there are two principles of approach. Passengers can be informed of the elevator to serve them when a certain length of time will elapse before the arrival of the elevator. On the other hand, passengers can be given an indication of the elevator to serve them within a certain time after the landing call was entered, in which case it will be possible for a person having pressed a landing call button to move to a better position to wait for a while and, when the signaling appears, walk back to the area in front of the elevator to be ready to enter. This approach may be easier for passengers to adopt. Thus, in addition to pure immediate allocation of landing calls, the method also contains a possibility for more flexible implementations. The above-described control method is suited e.g. for buildings where early signaling is required and, on the other hand, where the conception of the service standard of the elevators tends to be associated with the overall service received, e.g. in hotels. In this case, it will be an advantage if passengers can move with their luggage in time and without great haste to the area in front of the elevator to serve them. A corresponding need for early signaling is also encountered in large elevator systems, in which the walking distances to different elevators may be long.